Accurate application of a precontoured-locking plate for proximal humeral fractures in Asians: a cadaveric study.

OBJECTIVES: The purpose of this study was to identify the optimal position for a precontoured-locking plating (PHILOS(®)) of the proximal humerus in Asians in terms of conformity and to determine the prevalence of screw exits in the position of the highest conformity.

METHODS: Twenty adult humeri and 14 cadaveric shoulders were included in this study. After placing the precontoured plate in the well-fitted position on the humerus, we measured the distance between the upper margin of the plate and the tip of greater tuberosity (GT) (distance A) and the distance between the anterior margin of the plate and lateral border of the bicipital groove (BG) (distance B). The prevalence of K-wire exits was assessed. In the 14 cadaver shoulders, the mutual relation between the most inferior locking sleeve of the optimally positioned plate and the axillary nerve was evaluated to assess the potential for axillary nerve injury.

RESULTS: The precontoured plate was well-fitted and remained in a relatively constant position in all specimens. Distance A was an average of 3.6 mm (range 1.4-5.5 mm), and distance B was an average of 2.5 mm (range 0-4.6 mm). The K wire closest to the BG pierced it in four cases (20 %), and most inferior K wires exited at an average distance of 3.8 mm (range 1.6-9.0 mm) from the inferior articular margin of the humeral head. Regarding involvement of the BG, articular width was the only significant variable in the logistic regression model, with an odds' ratio of 0.610. The axillary nerve was located at an average vertical distance of 59.7 mm (range 51.8-66.9 mm) from the tip of the GT in a vertically neutral position. The results did not differ between the left and right sides (t = 0.326, p = 0.755). Although the axillary nerve was slightly inferior to the most inferior locking holes of the proximal humerus, it was located in the path of their locking sleeves on the deltoid muscle.

CONCLUSION: The optimal position for the highest conformity led to ideal fixation of the proximal humerus and inferomedial support screw in Asians. However, the precontoured plate sometimes had screw exits that involved the BG, and articular width had a large impact on involvement of the BG. If locking sleeves for the most inferior holes were introduced on the deltoid muscle in a neutral position, there was high potential for injury to the axillary nerve in Koreans.